Name:
Date:
Lab #:
Cellular Respiration in Yeast
Background: The purpose of any leavener is to produce the gas that makes bread rise. Yeast does this by feeding on
the sugars in flour, and releasing carbon dioxide in the process. While there are about 160 known species of yeast
(Saccharomyces cerevisiae) commonly known as baker's yeast, is the one most often used in the kitchen.
Yeast is tiny: Just one gram holds about 25 billion cells. That amount of fungi can churn out a significant amount of
carbon dioxide, provided it has the simple sugars it uses as food. Fortunately, yeast can use its own enzymes to break
down more complex sugar into a form that it can consume.
Most breads are made using YEAST. Believe it or not, yeast is actually living microorganisms! When bread is made, the
yeast becomes spread out in flour. Each bit of yeast makes tiny gas bubbles and that puts millions of bubbles (holes)
in our bread before it gets baked. When the bread gets baked in the oven, the yeast dies and leaves all those bubbles
(holes) in the bread.
Question: Does the type of “yeast food” affect the rate of cellular respiration?
How are we going to do this? To understand conditions that influence growth and cellular respiration in yeast. This will
be demonstrated by measuring the diameter of a balloon, which will indicate the amount of CO2 produced.
Materials:
1. Yeast
2. 1 tsp (4g) of Sugar, syrup, honey, vinegar, brown sugar, juice
3. Erlenmeyer Flasks (500 mL)
4. Beaker (1000 mL)
5. Graduated Cylinder
6. 1 Balloon
7. 2 feet of string
8. Ruler
Pre-Prep
1. Fill 1000 mL beaker with 800 mL of water and place on hot plate to LOW to make water warm (105-115 F)
2. Class Control group: 100mL warm water and _________________ of yeast
Each Group Will:
1. Obtain a balloon – blow the balloon up a few times to get it “stretchy”
2. Obtain a 250 mL Erlenmeyer Flask
3. Place 100 mL of warm water into the flask
4. Place ________________ of yeast into flask
5. Swirl the flask to mix contents
6. Place 1 tsp of your group’s assigned food into flask
7. Swirl the mixture again and QUICKY place the balloon over the top of the flask making sure the flask was sealed
8. Measure the circumference of the balloon in centimeters at 0 minutes and every 5 minutes for a total of 25
minutes.
 Do this by wrapping the string around the circumference of the balloon and measuring that distance it
wrapped around the balloon with a ruler

Record these measurements in the data on the next page
Circumference of the Balloon (in cm)
Time
(min)
Control
(No Food)
Sugar
Syrup
Honey
Vinegar
Brown
Sugar
Juice
0
5
10
15
20
25
1. Write the equation for cellular respiration
______
2. A) What yeast food resulted in the highest rate of cellular respiration? ______________________________________
B) Explain why you think this is the result:
3. What substance does yeast break down in cellular respiration?
4. A) What waste product is given off by yeast during cellular respiration?
B) How did we measure how much of this waste product was given off by the yeast?
5. Why do we use yeast to make bread?
6. What was the independent variable in this lab? _________________________________________________________
7. What was the dependent variable?